Conventionally, in film units for use in the photography of the multi-color diffusive transfer process type (hereinafter referred to as a film unit), there have already been proposed various types, and the typical type thereof is shown in FIGS. 1 to 5 of the accompanying drawings, which has already been disclosed in Japanese Laid Open Patent Publication (Tokkaisho) No. 50-153628. FIG. 1 is a top plan view of the film unit, while FIG. 5 is an exploded view showing the disassembled state of the components, in which the pod and trap ends have not been folded over yet. As can be seen from these FIGS. 1 and 5, the film unit comprising a plurality of laminated layers each contributing to a self-processing photographic function, including a first sheet 1, a second sheet 2, a mask sheet 3 defining an image border definition with an aperture provided therein, a rupturable container or pod (member) 4 containing an aqueous processing liquid, a trap (member) 5 capable of retaining therein the surplus processing liquid after the diffusion transferring process and a pair of spacers 6 for use in regulating the thickness of the processing liquid to be spread over a layer constituting the first sheet 1. More specifically, in the film unit of such self-processing photographic function, the first sheet 1 comprising layers each having the same dimensions and composed of processing material for its full dimensions is applied thereon, the following in sequence, i.e. the mask 3 having the rectangular aperture defining the image area, the respective pod 4 and trap member 3 on both transverse aperture-bordering planes 3d, 3c of the mask, the paired spacers 6, 6 on both sides of lateral aperture bordering planes 3a, 3b of the mask and the transparent cover sheet 2. Accordingly, the mask 3, the paired spacers 6, 6, respective pod 4 and the trap member 5 are sandwiched between the first sheet 1 and the cover sheet 2, in which the pod and trap ends of the mask 3 are both folded over in a manner such that these can form respectively the pod and trap with respective subsidiary members. Consequent construction of the film unit is adapted to cause the pod's content to be effectively spread over the first sheet 1 when subjected to pressure, with a result that the self-processing photographic functioning is thus effected. As will be easily understood from the description hereinbelow, the film unit having such construction tends to have the consequent deterioration in image quality on the periphery 12 (see FIG. 2) of the image border definition, i.e. the occurrence of dotted dirt 13 (see FIG. 4) caused by uneven concentration, after the completion of the self-processing functioning thereof under a pressure loading condition. Namely, when the mask 3 is applied upon the first sheet 1, a heat-sensitive bonding agent is conventionally used. Such being the case, it is very difficult to completely seal the entire faces being bonded to each other, and some portions 14 (see FIG. 3) therebetween remain unsealed. Due to such undesirable sealing state, the processing liquid 7 permeates through unsealed portions 14, FIG. 6, with the result of such occurrence of dotted dirts 13 as described above.
More specifically, according to conventional film units (e.g. that disclosed in Japanese Laid Open Patent Publication (Tokkaisho) No. 50-153628), the mask 3 superposed on the first sheet 1 is made of opaque material, so that the photosensitive laminate of the first sheet 1 is prevented from being exposed except for the portion inside the image border definition, which is defined by the aperture provided in the mask. Furthermore, in the thermal bonding operation between the first sheet 1 and the mask 3, the sealing operation can not be carried out at a high temperature under a high pressure condition, since such operational condition results in a bad influence on the photosensitive laminate, consequently resulting in the occurrence of such unsealed portions 14 as shown in FIG. 3. As far as such unsealed portions 14 are concerned, when these portions are full of the processing liquid, through the permeation thereof, these portions are developed to a maximum concentration level within the photosensitive laminate, with these portions being shielded from a radiation light and developed in the absence of the light exposure. Such non-exposed portions consequently appear as dots 13 of uneven concentration on the periphery of the image border definition. The occurrence of such deterioration in image quality is especially undesirable in the case where the consequent, photographic image is to have white or almost white image borders.
Accordingly, an essential object of the present invention is to provide a photographic film unit, which does not involve any consequent deterioration in image quality especially on the periphery of the image border.
Another important object of the present invention is to provide a photographic film unit of the above described type, which is adapted to have a construction capable of preventing the occurrence of dot-like dirt caused by the uneven processing liquid concentration on the periphery of the image border definition.
A further object of the present invention is to provide a photographic film unit of the above described type, which is simple in construction and, which is highly efficient in use.